sv 产生随机数

$urandom $urandom_range

virtual task run_phase(input uvm_phase phase);
    `uvm_info( get_name(), $sformatf("HIERARCHY: %m"), UVM_HIGH);
    forever begin
      seq_item_port.try_next_item(req);
      if ( req == null ) begin
        // Send random idle
        @(drv_vi.drv_cb);
        drv_vi.drv_cb.wb_adr_i  <= $urandom_range(255,0);
        drv_vi.drv_cb.wb_cyc_i  <= 1'b0;
        drv_vi.drv_cb.wb_stb_i  <= 1'b0;
        drv_vi.drv_cb.wb_dat_i  <= $urandom;
        drv_vi.drv_cb.wb_we_i   <= 1'b0;
      end
      else begin
        `uvm_info( get_name(), $psprintf("Wishbone Transaction: \n%0s", req.sprint()), UVM_HIGH)
        @(drv_vi.drv_cb);
        drv_vi.drv_cb.wb_adr_i  <= req.xtxn_addr;
        drv_vi.drv_cb.wb_cyc_i  <= 1'b1;
        drv_vi.drv_cb.wb_stb_i  <= 1'b1;
        drv_vi.drv_cb.wb_dat_i  <= req.xtxn_data;
        drv_vi.drv_cb.wb_we_i   <= req.xtxn_n;
        repeat (2)
          @(drv_vi.drv_cb);
        repeat (20) begin
          drv_vi.drv_cb.wb_adr_i  <= $urandom_range(255,0);
          drv_vi.drv_cb.wb_cyc_i  <= 1'b0;
          drv_vi.drv_cb.wb_stb_i  <= 1'b0;
          drv_vi.drv_cb.wb_dat_i  <= $urandom;
          drv_vi.drv_cb.wb_we_i   <= 1'b0;
          @(drv_vi.drv_cb);
        end
        seq_item_port.item_done();
      end
    end
  endtask : run_phase